1. Field of the Invention
This invention is in the field of metal laminates, and more particularly relates to metal laminate structures of nonferrous, noncorrosive metals.
2. Description of the Related Art
A number of conventional techniques exist for the bonding of metals to achieve composite or laminate products. One technique is forge welding, which is used for the manufacturing of compound steel, wherein two types of steel are bonded together in open atmosphere to produce a composite product. In order to achieve such a composite, plates or layers of steel are heated to a high temperature and pressed together, using a pressure sufficient to cause the plates to form a molecular bond. One of the advantages of forge-welding over other methods of joining metals is that the bond is achieved without the use of additional metal. This may be contrasted with arc welding, for example, where an electrode of a metal that is compatible with the metals to be joined is heated by the passage of an electric current, to melt and become part of the welded joint. This alters the chemical makeup of the metal at the joint. Physical characteristics, as well as the appearance of the joined parts are changed. While this may be desirable in some cases, in others it is not acceptable. A properly forge-welded joint is extremely strong while retaining all the physical characteristics of the component parts, as well as presenting an attractive (sometimes invisible) bond.
This type of forge-welding has been practiced for many years and is also known in the industry as pattern welding. Another common term for this technique is damascened forging, with steel made by this technique being referred to as Damascus steel. Knife blades made from Damascus steel have been used for many years and are valued for the decorative and artistic qualities, as well as for the high quality of the blade.
One of the benefits of Damascus or forge welded steel is that a blade made using this technique tends to enjoy the advantages of each of the component ingredients. For example, a steel alloy having a high degree of flexibility may be combined in alternating layers with an alloy having superior hardness. The result is a blade of great flexibility that also takes and holds a sharp edge. It is not fully understood how characteristics of individual alloys are imparted to such a composite, when a single alloy composed of the same ingredients and in the same proportions as the combination of the two component alloys does not, generally, capture the combination of characteristics. Nevertheless, the phenomenon has been known and exploited by master smiths for centuries.
Regrettably, the techniques used to make Damascus steel are only effective on a very limited group of steel products. Only those steels that have a very high workability and low alloy content are able to be worked with this process.
Currently the knife-making industry is limited to unalloyed or alloyed carbon steels for decorative composite materials. This means that these components or materials are prone to corrosion and can add significant weight to the final product. Forge welding of other metals has been attempted, without good results. For example, efforts to achieve a reliable forge welded laminate of titanium or titanium alloys has been generally unsuccessful.
In an attempt to forge-weld other steel alloy materials, different techniques have been attempted. See, for example, U.S. Pat. No. 5,815,790. This patent describes a technique in which two stainless steel materials, at least one of which is in powder form, are placed under isostatic pressure while being heated to a high temperature. Working with metals in powdered form is difficult and expensive.
Hot isostatic compaction, or hot isostatic pressing (HIP) is known in the industry, and used, for example, to form parts from metallic powders, including powders of steel, aluminum, and titanium. HIP requires a cylindrical pressure vessel into which the material to be processed is inserted. The interior of the vessel (and the material) is heated to a high temperature, and the atmosphere of the vessel is pressurized to pressures sufficient to compact a powdered metal into a solid form. The HIP process requires expensive machinery and has limits to the size of the parts that can be made thereby, since a pressure vessel capable of withstanding huge pressures is required for the process. The vessel must be internally insulated from the heat of the process, to prevent the extreme temperatures from weakening the walls of the vessel under pressure. As the size of the vessel increases in a linear manner, the required thickness and strength of the vessel walls increases exponentially. This places a practical limit on the maximum size of parts that can be produced. Currently, the maximum working size is on the order of around four feet in diameter. It will be recognized that, as the size increases, the cost of owning and operating such a device also increases. Additionally, the materials in a pressure vessel cannot be handled or manipulated in any way until the procedure is complete. These issue, individually or in combination, make the use of HIP expensive and complicated for small parts, and impossible for large ones.